/*
 * This file is part of "JTA - Telnet/SSH for the JAVA(tm) platform".
 *
 * (c) Matthias L. Jugel, Marcus Meißner 1996-2005. All Rights Reserved.
 *
 * Please visit http://javatelnet.org/ for updates and contact.
 *
 * --LICENSE NOTICE--
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 * --LICENSE NOTICE--
 *
 */
package de.mud.ssh;

import java.io.IOException;
import java.security.SecureRandom;

/**
 * @author Marcus Meissner
 * @version $Id: SshMisc.java 499 2005-09-29 08:24:54Z leo $
 */
public class SshMisc {
  /**
   * return the strint at the position offset in the data
   *  First 4 bytes are the length of the string, msb first (not
   *  including the length itself).  The following "length" bytes are
   *  the string value.  There are no terminating null characters.
   */
  static public String getString(int offset, byte[] byteArray) throws IOException {


    short d0 = byteArray[offset++];
    short d1 = byteArray[offset++];
    short d2 = byteArray[offset++];
    short d3 = byteArray[offset++];

    if (d0 < 0) d0 = (short) (256 + d0);
    if (d1 < 0) d1 = (short) (256 + d1);
    if (d2 < 0) d2 = (short) (256 + d2);
    if (d3 < 0) d3 = (short) (256 + d3);

    int length = d0 * 16777216  //to be checked
      + d1 * 65536
      + d2 * 256
      + d3;
    String str = ""; //new String(byteArray,0);
    for (int i = 0; i < length; i++) {
      if (byteArray[offset] >= 0)
        str += (char) (byteArray[offset++]);
      else
        str += (char) (256 + byteArray[offset++]);
    }
    return str;
  }

  static public byte getNotZeroRandomByte() {
    byte[] randomBytes = new byte[32];

    SecureRandom random = new java.security.SecureRandom(randomBytes);
    while (true) {
      random.nextBytes(randomBytes);
      for (int i = 0; i < randomBytes.length; i++)
        if (randomBytes[i] != 0)
          return randomBytes[i];
    }
  }

  static public byte[] addArrayOfBytes(byte[] a, byte[] b) {
    if (a == null) return b;
    if (b == null) return a;
    byte[] temp = new byte[a.length + b.length];
    for (int i = 0; i < a.length; i++) temp[i] = a[i];
    for (int i = 0; i < b.length; i++) temp[i + a.length] = b[i];
    return temp;
  }


  static public byte[] XORArrayOfBytes(byte[] a, byte[] b) {
    if (a == null) return null;
    if (b == null) return null;
    if (a.length != b.length) return null;
    byte[] result = new byte[a.length];
    for (int i = 0; i < result.length; i++) result[i] = (byte) (((a[i] & 0xff) ^ (b[i] & 0xff)) & 0xff);// ^ xor operator
    return result;
  }

  /**
   * Return the mp-int at the position offset in the data
   * First 2 bytes are the number of bits in the integer, msb first
   * (for example, the value 0x00012345 would have 17 bits).  The
   * value zero has zero bits.  It is permissible that the number of
   * bits be larger than the real number of bits.
   * The number of bits is followed by (bits + 7) / 8 bytes of binary
   * data, msb first, giving the value of the integer.
   */

  static public byte[] getMpInt(int offset, byte[] byteArray) throws IOException {

    byte[] MpInt;

    short d0 = byteArray[offset++];
    short d1 = byteArray[offset++];

    if (d0 < 0) d0 = (short) (256 + d0);
    if (d1 < 0) d1 = (short) (256 + d1);


    int byteLength = (d0 * 256 + d1 + 7) / 8;
    MpInt = new byte[byteLength];
    for (int i = 0; i < byteLength; i++) MpInt[i] = byteArray[offset++];
    return MpInt;
  } //getMpInt


  /**
   * Return a  Arbitrary length binary string
   * First 4 bytes are the length of the string, msb first (not
   * including the length itself).  The following "length" bytes are
   * the string value.  There are no terminating null characters.
   */
  static public byte[] createString(String str) throws IOException {

    int length = str.length();
    byte[] value = new byte[4 + length];

    value[3] = (byte) ((length) & 0xff);
    value[2] = (byte) ((length >> 8) & 0xff);
    value[1] = (byte) ((length >> 16) & 0xff);
    value[0] = (byte) ((length >> 24) & 0xff);

    byte[] strByte = str.getBytes();

    for (int i = 0; i < length; i++) value[i + 4] = strByte[i];
    return value;
  } //createString


  /**
   * This table simply represent the results of eight shift/xor operations for
   * all combinations of data and CRC register values. In other words, it caches
   * all the possible resulting values such that they won't need to be computed.
   */
  static private long crc32_tab[] = {
    0x00000000L, 0x77073096L, 0xee0e612cL, 0x990951baL, 0x076dc419L,
    0x706af48fL, 0xe963a535L, 0x9e6495a3L, 0x0edb8832L, 0x79dcb8a4L,
    0xe0d5e91eL, 0x97d2d988L, 0x09b64c2bL, 0x7eb17cbdL, 0xe7b82d07L,
    0x90bf1d91L, 0x1db71064L, 0x6ab020f2L, 0xf3b97148L, 0x84be41deL,
    0x1adad47dL, 0x6ddde4ebL, 0xf4d4b551L, 0x83d385c7L, 0x136c9856L,
    0x646ba8c0L, 0xfd62f97aL, 0x8a65c9ecL, 0x14015c4fL, 0x63066cd9L,
    0xfa0f3d63L, 0x8d080df5L, 0x3b6e20c8L, 0x4c69105eL, 0xd56041e4L,
    0xa2677172L, 0x3c03e4d1L, 0x4b04d447L, 0xd20d85fdL, 0xa50ab56bL,
    0x35b5a8faL, 0x42b2986cL, 0xdbbbc9d6L, 0xacbcf940L, 0x32d86ce3L,
    0x45df5c75L, 0xdcd60dcfL, 0xabd13d59L, 0x26d930acL, 0x51de003aL,
    0xc8d75180L, 0xbfd06116L, 0x21b4f4b5L, 0x56b3c423L, 0xcfba9599L,
    0xb8bda50fL, 0x2802b89eL, 0x5f058808L, 0xc60cd9b2L, 0xb10be924L,
    0x2f6f7c87L, 0x58684c11L, 0xc1611dabL, 0xb6662d3dL, 0x76dc4190L,
    0x01db7106L, 0x98d220bcL, 0xefd5102aL, 0x71b18589L, 0x06b6b51fL,
    0x9fbfe4a5L, 0xe8b8d433L, 0x7807c9a2L, 0x0f00f934L, 0x9609a88eL,
    0xe10e9818L, 0x7f6a0dbbL, 0x086d3d2dL, 0x91646c97L, 0xe6635c01L,
    0x6b6b51f4L, 0x1c6c6162L, 0x856530d8L, 0xf262004eL, 0x6c0695edL,
    0x1b01a57bL, 0x8208f4c1L, 0xf50fc457L, 0x65b0d9c6L, 0x12b7e950L,
    0x8bbeb8eaL, 0xfcb9887cL, 0x62dd1ddfL, 0x15da2d49L, 0x8cd37cf3L,
    0xfbd44c65L, 0x4db26158L, 0x3ab551ceL, 0xa3bc0074L, 0xd4bb30e2L,
    0x4adfa541L, 0x3dd895d7L, 0xa4d1c46dL, 0xd3d6f4fbL, 0x4369e96aL,
    0x346ed9fcL, 0xad678846L, 0xda60b8d0L, 0x44042d73L, 0x33031de5L,
    0xaa0a4c5fL, 0xdd0d7cc9L, 0x5005713cL, 0x270241aaL, 0xbe0b1010L,
    0xc90c2086L, 0x5768b525L, 0x206f85b3L, 0xb966d409L, 0xce61e49fL,
    0x5edef90eL, 0x29d9c998L, 0xb0d09822L, 0xc7d7a8b4L, 0x59b33d17L,
    0x2eb40d81L, 0xb7bd5c3bL, 0xc0ba6cadL, 0xedb88320L, 0x9abfb3b6L,
    0x03b6e20cL, 0x74b1d29aL, 0xead54739L, 0x9dd277afL, 0x04db2615L,
    0x73dc1683L, 0xe3630b12L, 0x94643b84L, 0x0d6d6a3eL, 0x7a6a5aa8L,
    0xe40ecf0bL, 0x9309ff9dL, 0x0a00ae27L, 0x7d079eb1L, 0xf00f9344L,
    0x8708a3d2L, 0x1e01f268L, 0x6906c2feL, 0xf762575dL, 0x806567cbL,
    0x196c3671L, 0x6e6b06e7L, 0xfed41b76L, 0x89d32be0L, 0x10da7a5aL,
    0x67dd4accL, 0xf9b9df6fL, 0x8ebeeff9L, 0x17b7be43L, 0x60b08ed5L,
    0xd6d6a3e8L, 0xa1d1937eL, 0x38d8c2c4L, 0x4fdff252L, 0xd1bb67f1L,
    0xa6bc5767L, 0x3fb506ddL, 0x48b2364bL, 0xd80d2bdaL, 0xaf0a1b4cL,
    0x36034af6L, 0x41047a60L, 0xdf60efc3L, 0xa867df55L, 0x316e8eefL,
    0x4669be79L, 0xcb61b38cL, 0xbc66831aL, 0x256fd2a0L, 0x5268e236L,
    0xcc0c7795L, 0xbb0b4703L, 0x220216b9L, 0x5505262fL, 0xc5ba3bbeL,
    0xb2bd0b28L, 0x2bb45a92L, 0x5cb36a04L, 0xc2d7ffa7L, 0xb5d0cf31L,
    0x2cd99e8bL, 0x5bdeae1dL, 0x9b64c2b0L, 0xec63f226L, 0x756aa39cL,
    0x026d930aL, 0x9c0906a9L, 0xeb0e363fL, 0x72076785L, 0x05005713L,
    0x95bf4a82L, 0xe2b87a14L, 0x7bb12baeL, 0x0cb61b38L, 0x92d28e9bL,
    0xe5d5be0dL, 0x7cdcefb7L, 0x0bdbdf21L, 0x86d3d2d4L, 0xf1d4e242L,
    0x68ddb3f8L, 0x1fda836eL, 0x81be16cdL, 0xf6b9265bL, 0x6fb077e1L,
    0x18b74777L, 0x88085ae6L, 0xff0f6a70L, 0x66063bcaL, 0x11010b5cL,
    0x8f659effL, 0xf862ae69L, 0x616bffd3L, 0x166ccf45L, 0xa00ae278L,
    0xd70dd2eeL, 0x4e048354L, 0x3903b3c2L, 0xa7672661L, 0xd06016f7L,
    0x4969474dL, 0x3e6e77dbL, 0xaed16a4aL, 0xd9d65adcL, 0x40df0b66L,
    0x37d83bf0L, 0xa9bcae53L, 0xdebb9ec5L, 0x47b2cf7fL, 0x30b5ffe9L,
    0xbdbdf21cL, 0xcabac28aL, 0x53b39330L, 0x24b4a3a6L, 0xbad03605L,
    0xcdd70693L, 0x54de5729L, 0x23d967bfL, 0xb3667a2eL, 0xc4614ab8L,
    0x5d681b02L, 0x2a6f2b94L, 0xb40bbe37L, 0xc30c8ea1L, 0x5a05df1bL,
    0x2d02ef8dL
  };





  /**
   * Compute the crc	Cyclic Redundancy Check, with the polynomial 0xedb88320,
   * The polynomial is X^32+X^26+X^23+X^22+X^16+X^12+X^11+X^10+X^8+X^7+X^5+X^4+X^2+X^1+X^0
   *  We take it "backwards" and put the highest-order term in the lowest-order bit.
   * The X^32 term is "implied"; the LSB is the X^31 term, etc.
   * The X^0 term (usually shown as "+1") results in the MSB being 1.
   * so the poly is 0x04c11db7 (used for Ethernet)
   * The buf will be the Padding, Packet type, and Data fields.
   * The crc is computed before any encryption.
   * R =X^n * M rem P		M message		P polynomial crc	R : crc calculated.
   * T(x) = x^n * M(x)  +  R(x)	property: T rem P = 0
   */



  // Return a 32-bit CRC of the byte using the feedback terms table

  static public long crc32(byte[] s, int len) {
    int i;
    long crc32val = 0;
    for (i = 0; i < len; i++) {
      crc32val =
        crc32_tab[(int) ((crc32val ^ s[i]) & 0xff)] ^ (crc32val >> 8);
    }
    return crc32val;
  }

}
